Prior art oil filters for filtering the lubricating oil of internal combustion engines, have been used satisfactorily for a long time in the past.
Such an oil filter typically comprises a casing connected in the oil flow and internally containing a filter element formed by a cylinder of pleated resin-impregnated filter paper with its axial ends cemented and sealed in circular end caps held apart by a perforated center tube. The casing's internal construction is designed so that normally the oil flow is radially inwardly, or outside in, with respect to the pleated paper cylinder.
In the case of an automobile engine oil filter, the minimum life expectancy demanded has been some 6,000 miles of automobile travel, and for this service life the prior art filters were adequate.
Now automobile manufacturers and the public are demanding an oil filter having a much more extended service life, exemplified by the current demand for a so-called 15,000 mile automobile oil filter.
When the conventional oil filter with its prior art resin-impregnated pleated paper element is subjected to such an extended use, the paper element with time may rupture and/or collapse. This trouble is exaggerated by the fact that today automobile engines operate at much higher temperatures than before, lubricating oil temperatures in the range of 300.degree. F. being commonly experienced.
Even in the past the same trouble was experienced when the pleated paper element was designed with unconventional pleat dimensions or when subjected to a pressure differential higher than was considered to be normal.
With the above in mind, the U.S. Royer et al. U.S. Pat. No. 3,334,753, Aug. 8, 1967, suggested the idea of a pleated element comprising two layers, the outer layer being the usual filter paper and the inner layer, pleated with the outer layer, comprising a rigid perforated wire material provided with openings bigger than the pores of the filter paper. Other rigid metal reinforcing members were incorporated. While this construction may have braced the paper layer against rupture or collapse, the obvious materials and manufacturing costs involved are commercially objectionable.
Ten years later the above concept is again suggested in the Pall U.S. Pat. No. 4,033,881, July 5, 1977. In this instance, the requirement for the rigid wall backing for the filter paper is repeated with emphasis. A rigid perforated metal wall is proposed. In addition, among other things, the use of spunbonded non-woven materials including those made of polyamide fibers is mentioned. The manner in which the patentee proposed to make such a material as rigid as metal, is not disclosed.
The object of the present invention is to provide a filter element particularly adapted for incorporation in an automobile engine oil filter and which will meet the current requirement for a 15,000 mile minimum service life but designed so that the filter materials and manufacturing costs are within commercially acceptable limits.